The present invention relates in general to an optical waveguide and more particularly to a semiconductor optical device, such as a laser diode or an optical modulator, having an optical waveguide made of semiconductor materials, a fiber optical amplifier and an optical transmission system.
A semiconductor optical device represented by a semiconductor laser has an optical waveguide which is mainly made of semiconductor materials and which serves; to confine an optical field and propagate therethrough light. This optical waveguide is manufactured in such a way that a plurality of semiconductor layers having different refractive indexes are laminated and then the resultant lamination structure is selectively etched away to form a pattern with several .mu.m width. In the optical waveguide, a cladding layer is doped with impurities so that a current can be injected into a core layer and also an electric field can be applied thereto. As a result, the various functions such as lasing, optical amplification, optical modulation and optical switching can be realized.